Hi S2j,
For $150.00 you can probably slap a PIII_1.4GHz in your computer. Then a Radeon 9700 Pro and you'll be CFS3 simming much better. Just a suggestion.
"The PL-iP3/T is an innovative upgrade adapter that enables Slot 1 systems (including those based on Intel Celeron, Pentium II, and Pentium III CPUs) to use the newer "Tualatin" Celeron and Pentium III CPUs. With the PL-iP3/T, you can obtain significantly faster performance (up to 1.4GHz) from your Slot 1 system--without replacing the motherboard."
http://plpadmin.tempdomainname.com/index2.htmlThen click on where it says "Desktop", then "Slot 1", then "PL-ip3/T". I think your 650 Duron is a slot 1. If it's a socket 370 then click on that.
If you run the "Quick CPU Upgrade Finder" there you can find out for sure. I upgraded my buddy's Gateway 450 with the PowerLeap PL-ip3/T, 1.4GHz and he's very pleased.
Good luck.